1. Field of the Invention
The present invention relates to a serial scanning type ink jet recording apparatus in which recording with a high image quality is consistent with full-color recording at a high speed, particularly to an ink jet head constitution for simultaneously realizing both the recording with a high image quality and the full-color recording at a high speed, and a maintenance method of the constitution.
2. Related Background Art
An ink jet recording apparatus is capable of forming an image by superimposition of three primary colors by cyan ink, magenta ink, and yellow ink, which is called subtractive color mixture. Furthermore, in addition to the three colors of ink, black ink capable of representing a high contrast, and light ink (light cyan ink, light magenta ink) whose content of a color material is lowered in order to raise gradation are used, and accordingly an output image having a photograph image quality can be obtained. Techniques such as miniaturization of ejected ink droplets and the like have also been introduced in order to reduce a grained state of the output image, and it is possible to form a high-quality image.
In recent years, for further enhancement of the image quality, special ink (in colors other than cyan, magenta, and yellow) representing a color gamut which cannot be reproduced by the above-described six colors of ink has been used, or color pigment ink for enhancing a keeping quality of the output image has been used. Alternatively, a solution or the like which is imparted or applied before or after the ink is ejected to a recording medium to enhance gloss, has been used.
For example, in Japanese Patent Application Laid-Open No. 2001-138552, an ink jet recording apparatus has been described which is provided with orange and green ink for expanding a reproducible color gamut, in addition to black, cyan, magenta, yellow, light cyan, and light magenta ink.
On the other hand, a printing speed for outputting the image has been rapidly raised by progress in a device (ink jet recording head, or scanning means for scanning a carriage on which the ink jet recording head is mounted) for ejecting the ink to the recording medium.
For example, in a serial scanning type ink jet recording apparatus in which a carriage is reciprocated/moved in a main scanning direction to perform the recording, the printing speed is raised by the following measures.
(i) A maximum response frequency of ink ejection at the time of the ejecting of the ink from the ink jet recording head is raised to increase a scanning speed of the carriage.
(ii) The number of nozzles which eject the ink is increased in the ink jet recording head. Concretely, when the number of the nozzles arranged in a direction (referred to also as a sub-scanning direction) crossing the scanning direction of the carriage is increased, a width recordable in one scanning time is increased. It is to be noted that the nozzles which eject the ink are also referred to as ejection ports.
(iii) Nozzle arrays of the color ink in the ink jet recording head are arranged symmetrically in the scanning direction, and reciprocating printing is performed using the ink jet recording head (described in Japanese Patent Application Laid-Open No. 2001-171119). Even when inks of the same color are mixed on the recording medium, when an order of colors to be attached to the recording medium changes, a difference is generated in a dyestuff attached state in the medium, and a color development property largely differs. To solve the problem, a color arrangement order is unchanged at the time of the scanning in either forward or backward direction. In this constitution, even when the scanning direction changes, the color arrangement order does not change, and therefore color unevenness by the color development difference is not generated.
However, since the ink jet recording apparatus is a system for converting input image data into the output image using a solution of ink as a medium, a maintenance technique is a very important element. Even when many types of ink are used for the enhancement of the image quality, or the device for ejecting the ink is developed in order to raise the printing speed as described above, it is a large technical problem to normally eject the ink from the ink jet recording head. Here, major problems requiring the maintenance technique will be briefly described.
(a) During the recording of the input image data, the ink evaporates in the ejection port which does not eject any ink among a plurality of nozzles arranged in the ink jet recording head, viscosity of the ink in the ejection port increases, the ink cannot be ejected stably with usual ink discharge energy, and an ejection defect is generated.
(b) During the recording, ink droplets ejected from the nozzle also include fine ink droplets (referred to also as mist) in addition to main ink droplets. When the fine ink droplets stick around the ink ejection ports of the ink jet recording head, a rectilinear property of the ink ejection is hampered.
(c) When bubbles exist in a portion of an ink reservoir in the ink jet recording head, a gas passed through the ejection port or a material constituting the ink jet recording head is incorporated into the bubbles to grow, or the bubbles expand by a temperature rise at the time of the printing. Therefore, ink supply from an ink tank is hampered. As a result, printing defects are generated.
Maintenance techniques for solving these problems (a) to (c) are as follows.
(a) A predetermined amount of ink is ejected to discharge the ink whose viscosity has increased, separately from the printing at a time when the image is formed on the recording medium, in accordance with a time, environment and the like in which any ink is not ejected (the operation will be hereinafter referred to as preliminary ejection).
(b) The number of ejection times when the ink droplets are ejected from the ejection ports is counted. When the counted number exceeds a predetermined value, a plane (hereinafter referred to as the face) in which the ejection ports of the ink jet recording head are formed is wiped with a rubber blade or the like to remove the attached ink (the operation will be hereinafter referred to as the wiping).
(c) The ink is drawn out from the ejection port using a pump, and a recovery operation is performed to discharge the ink in the ejection port (the operation will be hereinafter referred to as the suction recovery).
Furthermore, in the ink jet recording apparatus in which the ink jet recording head is separable from an ink tank and the ink tank is replaceable, the suction recovery is performed even after the replacement of the ink tank.
The wiping and the suction recovery will be briefly described with reference to the drawings.
FIG. 7 is a drawing showing the wiping. Reference numeral 1101 denotes a rubber blade which performs the wiping, 1102 is a surface (hereinafter referred to also as the face) to be wiped in which ejection ports are formed, 1103 denotes ink ejection ports, 1104 denotes attached ink which hampers the ejecting, and 1105 denotes a wiping direction. In the wiping, as shown, when the rubber blade 1101 pressed onto the ink jet recording head is moved in the direction 1105, the attached ink 1104 is brought into contact with the blade and wiped off the face.
FIG. 8 is an explanatory view of the suction recovery. Reference numeral 1201 denotes an ink jet recording head, 1202 denotes ink ejection nozzles, 1203 denotes a face, 1204 denotes a suction cap, 1205 denotes a tube for discharging the ink, and 1206 denotes a suction pump which generates a negative pressure to draw out the ink. In the suction recovery, in general, the rubber suction cap 1204 is allowed to abut on the face 1203 or brought into close contact with the face, the suction pump 1206 is rotated in a direction of an arrow 1207 to generate a negative pressure, and accordingly the ink in the ink jet recording head 1201 is drawn out into the suction cap 1204 via the ink ejection ports 1202, and discharged from the ink discharging tube 1205.
The above-described maintenance technique is largely influenced by an ink system selected in the ink jet recording apparatus, and especially system constitutions of the wiping and suction recovery techniques change. Next, this respect will be described.
(1) Ink System in which any Reaction is not Caused at the Time of Contact of the Ink
When the ink for use in the ink jet recording apparatus is all-color dye ink or all-color pigment ink, there is not any special problem even in mixture of different colors of the ink. Therefore, the rubber blade for use in the wiping, or the suction cap for use at the time of a recovery operation such as suction recovery can be integrated, and a system can be constituted of members common to all colors.
(2) Ink System in which any Reaction is not Caused at the Time of the Contact of the Ink and in which Black Ink is Used as Pigment Ink for Enhancing a Black Character Quality Level in Plain Paper
In general, the pigment ink is remarkably different from the color dye ink in ink jet ejection performance and maintenance property. Therefore, when the pigment ink is mixed into the ejection port of the dye ink, the ejection performance changes, and ejection defects are caused. Therefore, independent members or the same members as branched are used in rubber blade members in such a manner that the members do not contact each other at the time of the wiping. A system constitution is required in which at least two chambers are disposed in the suction cap in such a manner as to prevent the pigment ink from being mixed with the dye ink and in which the ink is discharged from another tube for discharging the ink.
(3) Ink System which Reacts to the Contact of the Ink
In a case of the printing on the plain paper having a low absorption fixing speed, when the black ink contacts the color ink, color mixture (referred to also as bleeding) occurs. To prevent this color mixture, ink which reacts to the contact of the pigment black ink with the dye color ink is sometimes used in order to prevent the color mixture from being caused even by the contact of the pigment black ink with the dye color ink. In this ink system, a system constitution in which the black ink does not contact the color ink in the rubber blade, suction cap section, or ink discharging tube section is required.
(4) Ink System in which a Special Solution Contacts and Reacts to the Ink
In this case, it is not preferable to bring the special solution into contact with the ink. Therefore, the system constitution in which the special solution does not contact the ink in the rubber blade or suction cap section is required in the same manner as in (3).
(5) Ink System in which the Special Solution does not React to the Ink in the Contact but Ink Properties Largely Differ
For example, in an ink system using a special solution containing a large amount of solids such as polymers and ink that does not contain any solid, the special solution is largely different from the ink in ejection performance. Therefore, when the special solution is mixed via the ejection port, the ejection performance temporarily drops. Therefore, the same system constitution as that of (3) is preferable. However, this is not limited in consideration of product costs.